package com.system.test.base;

public class SnowFlake {

	// 起始的时间戳
	// private final static long START_TIMESTAMP = 1480166465631L;
	private final static long START_TIMESTAMP = 1679634656467L;

	// 每一部分占用的位数，符号位不算在内
	private final static long SEQUENCE_BIT = 12; // 序列号占用的位数
	private final static long MACHINE_BIT = 5; // 机器标识占用的位数
	private final static long DATACENTER_BIT = 5; // 数据中心占用的位数

	// 每一部分的最大值
	private final static long MAX_SEQUENCE = ~(-1L << SEQUENCE_BIT);
	private final static long MAX_MACHINE_NUM = ~(-1L << MACHINE_BIT);
	private final static long MAX_DATACENTER_NUM = ~(-1L << DATACENTER_BIT);

	// 每一部分向左的位移
	private final static long MACHINE_LEFT = SEQUENCE_BIT;
	private final static long DATACENTER_LEFT = SEQUENCE_BIT + MACHINE_BIT;
	private final static long TIMESTAMP_LEFT = DATACENTER_LEFT + DATACENTER_BIT;

	private long datacenterId; // 数据中心
	private long machineId; // 机器标识
	private long sequence = 0L; // 序列号
	private long lastTimestamp = -1L;// 上一次时间戳

	public SnowFlake(long datacenterId, long machineId) {
		if (datacenterId > MAX_DATACENTER_NUM || datacenterId < 0) {
			throw new IllegalArgumentException("Datacenter ID can't be greater than MAX_DATACENTER_NUM or less than 0");
		}
		if (machineId > MAX_MACHINE_NUM || machineId < 0) {
			throw new IllegalArgumentException("Machine ID can't be greater than MAX_MACHINE_NUM or less than 0");
		}
		this.datacenterId = datacenterId;
		this.machineId = machineId;
	}

	/**
	 * 产生下一个ID
	 *
	 * @return 下一个ID
	 */
	public synchronized long nextId() {
		long currTimestamp = getTimestamp();
		if (currTimestamp < lastTimestamp) {
			throw new RuntimeException("Clock moved backwards. Refusing to generate id");
		}

		// 如果是同一时间生成的，则进行毫秒内序列
		if (currTimestamp == lastTimestamp) {
			sequence = (sequence + 1) & MAX_SEQUENCE;
			// 序列号已经达到最大值，下一个毫秒
			if (sequence == 0L) {
				currTimestamp = getNextTimestamp();
			}
		} else {
			// 时间戳改变，毫秒内序列重置
			sequence = 0L;
		}

		// 上次生成ID的时间截
		lastTimestamp = currTimestamp;

		// 移位并通过或运算拼到一起组成64位的ID
		return (currTimestamp - START_TIMESTAMP) << TIMESTAMP_LEFT // 时间戳部分
				| datacenterId << DATACENTER_LEFT // 数据中心部分
				| machineId << MACHINE_LEFT // 机器标识部分
				| sequence; // 序列号部分
	}

	/**
	 * 获取下一个毫秒数
	 *
	 * @return 下一个毫秒数
	 */
	private long getNextTimestamp() {
		long timestamp = getTimestamp();
		while (timestamp <= lastTimestamp) {
			timestamp = getTimestamp();
		}
		return timestamp;
	}

	/**
	 * 获取当前的时间戳
	 *
	 * @return 当前的时间戳
	 */
	private long getTimestamp() {
		return System.currentTimeMillis();
	}

	public static void main(String[] args) {
		
		SnowFlake snowFlake = new SnowFlake(1, 1);

		long startTime = System.nanoTime();

		for (int i = 0; i < 100000; i++) {
			System.out.println(snowFlake.nextId());
		}

		long endTime = System.nanoTime();

		System.out.println("用时：" + (endTime - startTime) / 1000000 + "ms");
	}
}